That would be because Mark is THE viltrumite with more potential that ever has been (he literally gets stronger by the minute, and his fight with Nolan also made him 10 times stronger), due to his genetic makeup, and because viltrumites lack adrenaline, they literally don’t have it, while Mark does, so he can get a little power up once his adrenaline kicks in.

Sadly, that only works with the viltrumites and their unfair ability to breed with anything